Abrading mixture

ABSTRACT

An abrasive mixture for abrading material from the surface of a workpiece is provided with improved cutting characteristics and lower temperature operating capability along with ease of cleaning through the inclusion of solid lubricant particles in the mixture including an inert powder matrix, abrasive particles and sufficient low vapor pressure water miscible liquid binder to provide a paste of a consistency desired for the intended operation. One mixture described includes mica particles as the solid lubricant in a clay powder matrix including abrasive particles such as silicon carbide along with a liquid glycollic compound binder.

United States Patent [191 Ceremsak et al.

[ June 11, 1974 1 ABRADING MIXTURE 521 05.0. ..s1/30s,51/309 s11 1nt.C1 C09g 1/02, C09g 1/06 58 FieldofSearch ..5l/308, 309,317,281

[56] References Cited UNITED STATES PATENTS 1,504,697 8/1924 Menard ...51/308 1,661,849 3/1928 Power....

1,739,631 12/1929 Cross 51/306 2,006,162 6/1935 Fuchs 51/308 3,053,694 9/1962 Daunt 51/308 3,421,872 1/1969 Anglin 51/30 Primary Examiner-Donald .1. Arnold Attorney, Agent, or Firm-Derek P. Lawrence; Lee H. Sachs [57] ABSTRACT An abrasive mixture for abrading material from the surface of a workpiece is provided with improved cutting characteristics and lower temperature operating capability along with ease of cleaning through the inclusion of solid lubricant particles in the mixture including an inert powder matrix, abrasive particles and sufficient low vapor pressure water miscible liquid binder to provide a paste of a consistency desired for the intended operation. One mixture described includes mica particles as the solid lubricant in a clay powder matrix including abrasive particles such as silicon carbide along with a liquid glycollic compound binder.

3 Claims, N0 Drawings ABRADING MIXTURE BACKGROUND OF THE INVENTION Radii of various sizes are required to be generated around the periphery of holes or channels in such precision. parts as the rotating turbine or compressor discs in gas turbine engines. One reason for such metal removal is to reduce areas of high stress concentrations which might result in premature failure of highly stressed components. Conventional grinding methods tend to leave residual stresses in the article at the point of grinding. In some instances, such as in the honing of internal passages or holes, the surfaces from which metal is to be removed is inaccessibleto conventional grinding apparatus.

Available are a number of honing compounds which can be passed over the surface from which metal is to be removed. However, such available compounds include liquid or semi-solid materials such as a matrix or lubricant in the form of oils, greases, putties, etc. Such materials have a tendency to adhere to the surfaces being abraded or honed and to abrasive particles included in the mixture. As a result, such oily or plastic lubricated materials reduce the abrasive particle action and can present workpiece cleaning problems. When an abrasive compound is used to hone internal surfaces of a workpiece and passes through relatively small channels or holes in the workpiece, the cleaning problem after honing can be particularly difficult.

SUMMARY OF THE INVENTION It is a principal object of the present invention to provide an abrasive mixture for honing which has improved cutting characteristics along with ease of cleaning from the workpiece.

These and other objects and advantages will be more clearly understood from the following detailed description and examples which are intended to be typical of rather than limiting on the scope of the present invention.

Briefly, the present invention provides an abrasive honing mixture which includes solid lubricant particles rather than a liquid lubricant. In one form, the mixture consists essentially of, by volume, a clay powder, preferably 5-25 parts; abrasive particles, preferably 25-45 parts; along with solid lubricant particles, preferably 25-30 parts; and sufficient low vapor pressure water miscible liquid, preferably a glycollic compound, to form a paste.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The surface characteristics of precision components used under relatively highly stressed conditions in modern gas turbine engines is an important consideration in determining component operating life. Whereas radii of sufficient size can be designed for a component such as a turbine or compressor disc, the available metal removal methods have been found to be unsatisfactory in one aspect or another: they preclude the development of true radii, or radii of sufficient size; they result in residual surface stresses; they present difficult cleaning problems for internal surfaces; or they are very time consuming and expensive for practical application. It has been found through the present invention that with a combination of a matrix, abrasive and lubricant, all in dry particulate form, along with sufficient water miscible low vapor pressure binder to form a paste, there can be provided a material which exhibits not only superior fiow characteristics but also faster cutting action along with ease of cleaning. Also, it has been found that radii more closely approaching true radii can be generated. Another improvement which has been recognized and attributed to the use of dry solid lubricant particles is that the temperature rise of the mixture, apparently due to internal friction under conditions of continuous use, is significantly less than that exhibited by available putty mixtures. Accordingly, break down of the components of the mixture is reduced and complicated machine cooling mechanisms are eliminated from the apparatus in which the honing is conducted.

The present invention in its preferred form comprises (a) a colloidal clay powder such as bentonite as a matrix or carrier and preferably in the range of about 5-25 parts by volume, (b) solid lubricant particles such as of mica to improve mixture flow and to reduce internal I friction within the matrix and preferably in the range of 25-30 parts by volume, (c) abrasive particles such as silicon carbide, boron nitride, diamond, aluminum oxide, etc., and preferably in the range of about 25-45 parts by volume, (d) with the balance a low vapor pressure liquid to avoid evaporation and hence hardening of the matrix and miscible with water for ease of cleaning, for example, a glycollic compound such as ethylene glycol. Amounts in the range of 20-30 parts by volume along with the quantities of materials described above has been found to be particularly useful.

During evaluation of the present invention, a mixture was prepared from the following ingredients:

Mixture Ingredients Parts by Volume Clay Western Bentonite 14.3 Solid Lubricant White Mica Powder 28.5 Abrasive Silicon Carbide 28.5 Ethylene Glycol 28.5

In relation, one to the other, the above ingredients were thus combined in the range of two parts by volume each of mica, silicon carbide and ethylene glycol with one part by volume of western bentonite. The mixture was prepared by blending to reasonable uniformity.

This mixture was then moved over areas where metal removal was desired until the required surface condition was fulfilled. For example, gas turbine engine nozzle segments were mounted in a fixture which was placed in a chamber including the above described mixture. The fixture carrying the segment was then reciprocated within the mixture until desired surface characteristics were produced. In one example, a nozzle segment in the cast condition had a surface finish of 50-80 RMS. After reciprocal movement through the above described media for a period of about minutes, a surface finish of 2-10 RMS was attained.

After removal from the mixture, excessive abrasive mixture can be removed easily from the article, even one havinginternal cavaties, by first blowing excessive mixture from the article with air and then washing the article in water.

Although the present invention has been described in connection with the specific mixture example above, it will be readily understood by those familiar with abrasive metal removal that a variety of abrasives can be used along with various other types of clays, solid lubricants and low vapor pressure, water miscible binders. Some examples of the many available abrasive particles have been given above. Other solid lubricants include graphite, molybdenum disulfide, etc. However, the solid lubricant should be selected to be compatible with the article being treated so as not to create corrosive conditions as might result through the use of a sulphur bearing compound with some of the nickel base alloys. Mica has been selected as the preferred embodiment because it generally is relatively low in sulfur'content and is available as a clean, dry lubricant.

What is claimed is:

parts silicon carbide and 2 parts ethylene glycol. 

2. The abrasive mixture of claim 1 in which the alkylene glycol is ethylene glycol included in the range of 20-30 parts by volume.
 3. The abrasive mixture of claim 2 consisting essentially of, by volume 1 part bentonite, 2 parts mica, 2 parts silicon carbide and 2 parts ethylene glycol. 